The invention relates to a method for the management of fragment ion spectra of a progenitor ion for any number of isolation and fragmentation generations, whereby the management comprises the preparation of the measurement of a spectrum, as well as memory management and the recalling of fragment ion spectra of a progenitor ion.
High frequency quadrupole ion traps as invented by Wolfgang Paul consist of a high-frequency supplied ring electrode and two end cap electrodes; ions can be stored inside. The ion traps can be used as a mass spectrometer by ejecting the ions selectively according to mass and measuring them by means of secondary-electron multipliers. There are several different methods known for ion ejection, which will not be discussed here in any further detail. Ion cyclotron resonance mass spectrometers are a different type of ion trap in which ions can be stored in a magnetic field of high constancy and additional electric fields. Herexe2x80x94after excitationxe2x80x94the circular movements of ions can be used to measure the ratio of their mass to their charge.
Ion trap mass spectrometers have special features which make their use interesting for many types of analysis procedures. In particular, selected ion types (so-called xe2x80x9cparent ionsxe2x80x9d) can be isolated in the ion trap (freed of all other ion types and stored alone) and, with the help of a damping or collision gas, can be fragmented by molecular collisions after excitation of their oscillating movements. This excitation to fragmentation occurs, for example, in quadrupole ion traps by applying an alternating current of an appropriate frequency to the end caps. The spectra of these fragment ions are known as xe2x80x9cdaughter ion spectraxe2x80x9d of the associated parent ions.
These daughter ion spectra contain information about the molecular structure of the ejected parent ions since they have come from them as fragments. xe2x80x9cGranddaughter ion spectraxe2x80x9d can also be measured as fragment ion spectra of selected daughter ions. In this way the structural information is increased. In favorable cases, it is possible to measure such fragment ion spectra up to the tenth generation and beyond. The original ion for this sequence of generations is called a xe2x80x9cprogenitor ionxe2x80x9d here.
Although each individual spectrum measured in such a way offers only relatively little information regarding the structure of the original ions, the entirety of all fragment ions of a progenitor ion does contain a large amount of structural information about the progenitor ion, particularly for the reason that the relationship of the origin of the fragment ions among each other is known. For good structural determination of the progenitor ion, however, it is generally necessary to measure, store and evaluate a larger number of fragment ion spectra.
Preparing the measurement method for these daughter ion spectra over several generations is laborious and has been possible up to now only interactively on the video screen during the measurements. For this purpose, daughter ion spectra are measured and visually evaluated. The user decides, based on his experience, from which daughter ion type he wishes to measure a granddaughter ion spectrum. He derives the mass of these daughter ion types from the representation of the daughter ion spectrum on the screen, then he enters this mass into a table (or subtable) for measurement of granddaughter ions. Once the granddaughter ion spectrum has been measured, he then possibly continues to measure several great-granddaughter ion spectra of several granddaughter ion types from the granddaughter spectrum.
This method is relatively simple if only one single spectrum each from the next generations is to be measured. The table is then linear, and every line corresponds to a generation. However, the method becomes very complicated if several fragment ion spectra of several (sister) ion types also need to be measured in every generation. That is why suppliers of mass spectra offer prepared table structures for some selected cases, but these fall far short of the actual demand.
The fast interactive control of measurement methods using xe2x80x9cintuitive actionsxe2x80x9d via the monitor is becoming more and more important in mass spectrometric application areas. The software with the simplest and clearest operation is increasingly the deciding factor when buying an expensive spectrometer.
Here, xe2x80x9cintuitive actionsxe2x80x9d signify those control actions which are so easily accessible to the user that he can remember and perform them independently after seeing them once, and thus require very little effort. Especially significant are those actions which are also performed in the same, or at least a similar way, in other programs which the operator uses daily.
The interactive control of complex measurement and evaluation methods is frequently conducted using the mouse. However, a changeover to keyboard operation is often unavoidable with the prior art in those methods, for example when a daughter ion spectrum must be scanned for an ion type depicted as a mass spectrometric peak. It is then necessary, with the prior art, to read the mass of the ion peak (for which there are usually mouse-controlled tools in specific display windows) and to enter this mass in a table for scanning fragment or daughter ions.
The changeover from mouse to keyboard for these interactive controls is felt to be bothersome, slow and nonergonomic to an increasing degree.
It is the objective of the invention to find an input and management method for the measurement, storage and retreaval of fragment ion spectra from a progenitor ion over several generations that can also handle family tree structures of any complexity, that can be controlled in a simple manner via the mouse, if possible, and which is very easy for the user to understand.
It is the basic idea of the invention to use the well-known xe2x80x9ctree viewxe2x80x9d, used to manage files in directories and subdirectories, likewise to manage fragment ion spectra of the descendant (or offspring) ions from a progenitor ion, and to easily prepare measurement methods for such fragment ion spectra. Thus it becomes easy to manage fragment ion spectra through several isolation and fragmentation generations, and to retrieve the stored spectra. Closer observation shows that the family trees of daughter and granddaughter spectra have the same structure as those of files in directories and subdirectories, and the setup and retrieval structures are similar. Tools and graphic representations for the file structures are readily available. The user is well acquainted with the display and use of the structures, for example from the File Manager (Windows 3.11) or Explorer (Windows 95, Windows 98 and Windows NT) from Microsoft, but also from many other programs. Each file has its exact position in a directory hierarchy which can be opened and closed in its representation by tree branches and branch generations. By clicking the mouse on the small box with a plus sign in the structure depicted by dotted lines, a further branch of the familiy tree can be opened to show a new generation of subdirectories.
It is a further idea of the invention to enter the notation of a fragment ion spectra automatically into this family tree. If a peak in an ion spectrum is clicked on, a context menu is opened in which the entries xe2x80x9cSchedule daughter ion spectrumxe2x80x9d and xe2x80x9cMeasure daughter ion spectrumxe2x80x9d are located. If one of these entries is activated by clicking the mouse, an additional entry takes place automatically at the correct position in the family tree for the daughter ion spectrum. If the correct measurement mode has been switched on, or if the xe2x80x9cMeasure daughter ion spectrumxe2x80x9d entry was activated, the corresponding spectrum is automatically measured. Alternatively, the peak of the mass spectrum can be simply dragged into the window for the daughter ion family tree simply by clicking on it and dragging it (with the mouse key depressed) into the tree view window. Once the mouse key is released, an entry is made at the correct position and, if the measuring mode is switched on, the spectrum is also measured automatically. The peak may need to be selected beforehand here by marking or highlighting, and this selection is also done using the mouse.
The entry may consist of a clickable icon and a text line which also contains the mass number. The mass number indicates the mass (in atomic mass units) of the direct parent ion for which this daughter ion spectrum is to be or was measured. The entries from daughter ion spectra of a parent ion are arranged according to these mass numbers. This parent ion can be of course, by itself, a daughter ion in a daughter ion spectrum of a higher-level parent ion (grandparent ion), that for its part may again be a daughter ion of a higher-level progenitor ion. The progenitor ion itself, together with other progenitor ions, may belong to a higher-level spectrum, and finally even several spectra may be displayed in this structure window.
Activating an icon for a daughter ion spectrum can trigger several actions, depending on the mode switched on. In a measuring mode for cyclical measurement of all fragment ion spectra, this activation means that the daughter ion spectrum belonging to the icon is to be displayed continuously without being interrupted by the display of other measured fragment ion spectra. Then, for example, further peaks may be selected for measurement of daughter ions. If no measurements are taking place, activation means that this spectrum has to be loaded from memory and displayed on the screen. In a measurement mode for a single measurement of fragment ion spectra, the activated fragment ion spectrum is measured once and displayed. In a measurement mode for repetitive measurements of a fragment ion spectrum, this spectrum is measured a number of times and averaged. Then a management window with input fields for the measurement parameters is displayed, via which the parameters for this measurement can be set and optimized.